It can be appreciated that exercise devices have been in use for years and include devices that simulate walking or jogging such as cross country ski machines, elliptic motion machines, and pendulum motion machines. Also included are exercise devices that simulate climbing such as reciprocal stair climbers.
Elliptic motion exercise machines provide inertia that assists in direction change of the pedals, which makes the exercise smooth and comfortable. However, rigid coupling to a crank typically constrains the elliptic path to a fixed length. Therefore, the elliptic path may be too long for shorter users, or too short for tall users. Further, a running stride is typically longer than a walking stride, so a fixed stride length does not ideally simulate all weight bearing exercise activities. Therefore, typical elliptic machines cannot optimally accommodate all users. Some pendulum motion machines may allow variable stride length, but the user's feet typically follow the same arcuate path in both forward and rearward motion. Such a motion does not accurately simulate walking, striding, or jogging, where the user's feet typically lift and lower. Reciprocal stair climbers typically allow the user to simulate a stepping motion, but that motion is generally constrained to a vertically oriented arcuate path defined by a linkage mechanism. Such a motion does not accurately simulate a wide range of real world climbing activities such climbing stairs or climbing sloped terrain.
More recently, variable stride exercise devices utilizing crank systems have been developed. These devices, however, may be complex and have high manufacturing costs.